Red dwarfs form just like other stars: out of a rotating cloud of gas and dust brought together via gravity and that reaches temperatures hot enough to fuse elements. But these stars are less than half as massive as our own sun—sometimes as little as 7.5 percent as massive—and as a result, burn much cooler and shine less brightly.
That low temperature may seem like a setback for a star, but it's the key to a red dwarf's longevity. It means that they don't burn through hydrogen that quickly, and burning through hydrogen is what will kill a star. So while stars like our sun might survive for around 10 billion years, red dwarfs have the potential to live out their days over trillions of years. Once their time is up, they'll become white dwarfs, but because our universe is only 13.8 billion years old, that hasn't happened yet.